Plant-based Wastewater Treatment

Local and National Policymakers, Irish Water, EPA (Environmental Protection Agency)

Courtesy: Féidhlim Harty (FH Wetland Systems)

Wastewater is any water that has been adversely affected in quality by human influence. Sewage is the most well known type of wastewater but others include: storm water (rainwater from roofs, car parks, roads, paths, etc.), greywater (e.g. sinks, showers, baths, washing machines and dishwashers), industrial effluents and farm yard washings. Plant-based technologies such as constructed wetlands and reed beds can be used to treat wastewater in ways that can be less expensive and more environmentally sustainable than conventional methods of effluent treatment.

A constructed wetland (or free water constructed wetland) is a purpose-built soil based marsh system in which the wastewater flows over the soil substrate. It consists of a fully plastic or clay-lined series of marshes planted with appropriate wetland plants. These filter the water and make it acceptable for discharge. The slow movement of water allows nutrient-rich sediment to settle out to the base of the system. The bacteria living in the wetland feed on the nutrients in the wastewater.

A reed bed (or gravel reed bed treatment system) is a gravel-based system in which the wastewater flows vertically or horizontally through the gravel substrate. It works in a similar way to a constructed wetland but may require a pump to operate correctly.

There are many advantages to plant-based treatment systems over conventional systems of effluent treatment including:
– Low construction and running costs. These systems avoid the need for large amounts of concrete, steel, mechanical and electrical equipment, etc.
– Easy management.
– Potential for efficient removal of a wide range of pollutants. They have a wide range of applications.
– No chemicals are necessary for these systems to operate.
– Tolerant of variable loads. Most can function effectively with a variable waste load (e.g. schools or caravan sites where the usage is seasonal)
– Wildlife habitat creation. Most of these systems provide shelter for insects and birds adding interest and beauty to gardens and other landscapes.
– More visually attractive. The plant growth, coupled with the wildlife that these systems can attract, makes them aesthetically pleasing. This can be important in a scenic area.
– May be used in conjunction with old or overloaded systems to achieve high discharge standards.
– Low energy solution. Unless they use pumps, these kinds of systems can need little or no energy to function as many use gravity to aid the flow of the water.
– Wood by-product. Plants used in some of these systems, such as willow, can be coppiced for wood fuel or chipped for landscaping.
– Systems such as a zero discharge willow facility have no discharge into the surrounding environment. This is useful when local discharging is not permitted.

These maturing technologies are demonstrating their effectiveness and becoming more widely accepted. Across the world, single houses, housing estates, campsites, hotels, farms, industrial facilities and municipal systems are increasingly employing these plant-based methods for treating wastewater and for other applications such as flood and drought prevention. Plant-based technologies have the potential to form a major part of the solution to wastewater treatment in Galway (e.g. at the proposed new housing development at Ardaun).